1. Field of the Invention
The present invention relates to a treatment composition for steel rebar embedded in concrete, and particularly to a treatment composition for applying to the surface of steel rebar prior to embedding in concrete to provide protection against corrosion of the steel.
2. Description of the Related Art
Steel rebar is commonly used for the reinforcement of concrete. Typical manufactured steel rebar is often coated with black oxide (i.e., “mill scale”), which is a mixture of three phases of iron oxide, namely wüstite (FeO) near the steel surface, magnetite (Fe3O4) above the layer of wüstite, and a top portion of the scale formed from hematite (α-Fe2O3). These layers of iron oxides develop cracks, since their coefficients of expansion and compaction due to changes in temperature differ to a significant extent than those of the steel structure.
Rebars covered in mill scale, along with rust, are falsely considered to provide protection against corrosive attack on their surfaces when embedded in concrete. The presence of the mill scale actually accelerates corrosive reactions. This is due to the cracks which form in the scale, as well as the presence of unstable oxides of iron. Both the cracks and the unstable iron oxides are conducive to the formation of galvanic cells which accelerate corrosive reactions in the rebar.
Due to the problems associated with mill scale, descaling of the rebar prior to its embedding in concrete may be performed. Although descaling improves the general corrosion resistance of the rebar, and also increases the threshold chloride concentration for the onset of a corrosion pitting attack, the process of descaling (typically conducted on-site) is very expensive, time consuming and requires cumbersome equipment. Other methods include surface coating, the usage of corrosion inhibitors, and the application of cathodic protection. However, the compositions and methods involved for each of these techniques are not only expensive but have a tendency to affect the quality of the concrete, as well as the bond strength between the concrete and the rebar.
Thus, an anti-corrosion treatment composition for steel rebar embedded in concrete solving the aforementioned problems is desired.